The danger of unwanted air emboli persists in many medical procedures. Before fluid can safely be introduced into the body, entrained gases must be removed. Certain procedures such as blood oxygenation present the risk of embolism. However such procedures have become routine in the operating room. Blood oxygenation is required whenever heart or lung surgery is being conducted, or when a blood stream is directed to an extracorporeal treatment circuit. During open heart surgery, for example, the natural cardiovascular function of the heart and lungs is suspended. The blood is then oxygenated artificially to replace the contained carbon dioxide.
Many types of blood oxygenators are known. One type, known as a membrane oxygenator, comprises first and second conduits separated by a gas transfer membrane permeable to oxygen and carbon dioxide. Oxygen bubbles, or emboli, are undesirable in such systems. However, such entrained gases often are present in the oxygenator circuit and adversely impact on apparatus set up time. For example, some commercially available blood oxygenator circuits have priming times of up to one hour. During oxygenator setup, initial oxygenator priming is done with saline priming solution. Air bubbles may be present in the priming circuit. Therefore, one goal during priming is the removal of gas bubbles in the line.
However, the danger of bubble formation in oxygenation circuits is not restricted to priming. For example, bubbles may be formed and enter the oxygenator circuit during an operation due to bad connections in the blood circuit, by suction of blood and debris from the chest cavity, or the improper set up of the oxygenator or pressure drop through the blood circuit.
Devices are known to address these embolism problems. One class of known devices uses density gradients and gravity to separate relatively large emboli. As the gas bubbles, once separated from the fluid flow, agglomerate and rise upward in fluid flow, ball valve or bubble trap devices effectively remove large emboli from the flow. Some known bubble traps use a non-woven material encasing a foam core which disengages bubbles from the blood flow. The bubbles, once separated from the fluid flow, agglomerate and rise to the top of the trap, and are vented. However, these devices do not remove emboli smaller than the mesh openings. In addition, the priming time with these devices is still unduly long, up to about one hour.